1. Field of the Invention
This invention relates to contact lenses and, more particularly, to a novel and highly-effective daily-wear and extended-wear contact lens and to a method and material for its manufacture.
2. Description of the Prior Art
There is a great need for a contact lens that can be worn safely, comfortably and continuously for an extended time, for example one or two months, and that is inexpensive enough to be discarded after that time. It is essential that such a lens be highly oxygen permeable, since the pupil of the eye has no blood circulation and extracts the oxygen needed by its cells directly from the atmosphere. Ideally, such a lens should be hard so that it can correct for astigmatism. In order to be comfortable for the wearer, however, the lens must also be hydrophilic; that is, the contact angle of an air-water interface with a surface of the lens must be small.
In conventional practice, measures taken to increase oxygen permeability increase contact angle, so that the lens becomes uncomfortable, and measures taken to reduce contact angle reduce oxygen permeability, so that the lens cannot be worn continuously for an extended period. This trade-off has thus far defeated efforts to produce an extended-wear contact lens having all of the desired properties.